1. Field of the Invention
This invention relates to a semiconductor device and a solid state imaging device, having a construction in which a semiconductor chip is mounted on the bottom of a hermetic sealed box-shaped resin-molded package.
2. Description of the Related Art
FIG. 1 shows a existing solid state imaging device in the related art comprising a CCD chip, used as a solid state imaging element 102, bonded with an adhesive 103 to the bottom surface in a cavity 101a of a resin-molded box-shaped package 101. Integrally extending from the package 101 are outer leads 104 and inner leads 105. Inner leads 105 are connected to a bonding pad (not shown) of the CCD chip 102 by wires 106. Thus, the outer leads 104 are electrically connected to the CCD chip 102. A transparent cap 107 of optical glass, for example, is bonded to the upper end of the package 101 by an adhesive 108 to hermetic seal the interior of the package 101.
A problem with the solid state imaging device in the related art is a bad moisture resistant property. The package 101 cannot effectively prevent infiltration of moisture into the cavity 101a through the bottom wall of the package 101. There is another solid state imaging device in the related art shown in FIG. 2, which has an improved moisture resistance.
In the solid state imaging device of FIG. 2, a part (called a depressed portion) of a lead frame used to make outer leads 104 and inner leads 105 is embedded under a cavity 101a of a resin-molded box-shaped package 101 to form a moisture resistant plate 109. In the other respects, the device of FIG. 2 is the same as the solid state imaging device of FIG. 1.
In the solid state imaging device of FIG. 2, the moisture resistant plate 109 prevents infiltration of moisture through the bottom of the package 101 into the cavity 101a, and thus improves the hermetic seal property of the solid state imaging device.
Another problem with the solid state imaging devices shown in FIGS. 1 and 2 is that the CCD chip 102 is bonded to the bottom in the cavity 101a of the package 101 which is made of a resin having a low thermal conductivity (for example, 2.1xc3x9710xe2x88x923cal/cm.s.xc2x0C.), resulting in that the heat generated from the CCD chip 102 during its operation is shut in the package 101 and increases the temperature of the CCD chip 102. An increase in temperature of the CCD chip 102 causes an increase in level of defects having a temperature characteristic and hence causes a deterioration in quality of images obtained by the solid state imaging devices.
The high temperature problem of chips during operation explained with reference to solid state imaging devices also applies to semiconductor devices, in general, using a package similar to the package 101.
It is therefore an object of the invention to provide a semiconductor device which is alleviated in temperature increase of its semiconductor chip during operation.
It is another object of the invention to provide a solid state imaging device which is alleviated in temperature increase of its solid state imaging element during operation.
According to the invention, there is provided a semiconductor device having a semiconductor chip mounted on a bottom surface of a cavity of an hermetic sealed box-shaped resin-molded package, comprising:
a radiator plate provided in a bottom wall of the package under the cavity or on the bottom surface of the cavity; and
the semiconductor chip and the radiator plate being bonded with an adhesive having a larger thermal conductivity than that of the resin forming the package.
According to the invention, there is also provided a solid state imaging device having a solid state imaging element on a bottom surface of a cavity in a hermetic sealed box-shaped resin-molded package, comprising:
a radiator plate provided in a bottom wall of the package under the cavity or on the bottom surface of the cavity; and
the solid state imaging element and the radiator plate being bonded with an adhesive having a larger thermal conductivity than that of the resin forming the package.
According to the invention, there is further provided a semiconductor device having a semiconductor chip on a bottom surface of a cavity in a hermetic sealed box-shaped resin-molded package, comprising:
a radiator plate which is a part of a lead frame, the radiator plate being provided in the bottom wall of the package under the cavity or on the bottom surface of the cavity; and
the semiconductor chip and the radiator plate being bonded with an adhesive having a larger thermal conductivity than that of the resin forming the package.
According to an aspect of the invention, the radiator plate is embedded in the bottom wall of the package under the cavity, and the semiconductor chip or the solid state imaging element is bonded to the radiator plate with the adhesive through an aperture formed in the bottom wall of the package in the cavity for access to the radiator plate.
According to another aspect of the invention, the radiator plate is provided on the bottom surface of the cavity, and the semiconductor chip or the solid state imaging element is bonded onto the radiator plate with the adhesive.
Usable as the resin forming the package are, for example, thermoset resins including epoxy resin, polyimide, silicone resin, phenolic resin, unsaturated polyester resin, and so forth.
The adhesive having a larger thermal conductivity than the resin of the package may include epoxy resin, imide resin, silicone resin or acrylic resin, for example, as its base material. Typically, the adhesive additionally contains a filler of silver (Ag) or other metal to increase the thermal conductivity.
When the radiator plate is provided on the bottom surface of the cavity in the package and the semiconductor chip or the solid state imaging element is bonded to the radiator plate with the adhesive, reflection of light from the surface of the radiator plate may adversely affect the operation of the semiconductor device or the solid state imaging device. To prevent this, the radiator plate is preferably coated with a light absorptive material such as chromium (Cr). Alternatively, reflection of light by the radiator plate can be prevented by adding a black pigment such as carbon to the adhesive and by applying the light absorptive adhesive to the surface of the radiator plate.
In a typical embodiment of the invention, the resin forming the package is epoxy resin, and the adhesive having a larger thermal conductivity than the resin of the package is epoxy resin containing a metal filler.
The radiator plate is typically a part of the lead frame, but may be a member independent from the lead frame. In the latter case, the radiator plate is bonded onto the bottom surface of the cavity of the package with the adhesive. Here again, the adhesive has a larger thermal conductivity than the resin of the package.
The radiator plate typically has a larger dimension than the semiconductor chip or the solid state imaging element for more effective radiation of heat.
The semiconductor device may be a solid state imaging device incorporating a solid state imaging element chip such as CCD chip, or may be a semiconductor IC device incorporating an IC chip or an LSI chip.
In the semiconductor device according to one or other aspect of the invention, heat from the semiconductor chip or the solid state imaging device during operation is quickly transferred to the radiator plate via the adhesive having a larger thermal conductivity than the package and is effectively radiated from the entirety of the radiator plate. Therefore, the temperature of the semiconductor chip or the solid state imaging element remains moderate during operation.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.